Fast, powerful, low-noise optical pumping of an atomic vapor with semiconductor optical amplifiers

TL;DR

This paper demonstrates that semiconductor optical amplifiers can efficiently generate low-noise pulsed optical pumping for atomic vapor magnetometers, achieving high sensitivity and longer coherence times.

Contribution

It introduces a novel use of semiconductor optical amplifiers for optical pumping in atomic vapor magnetometers, with comparable noise performance and improved sensitivity.

Findings

SOA-based optical pumping achieves nearly identical sensitivity to traditional methods.

Longer coherence times observed with SOA-AM compared to FM method.

Environment-limited sensitivity of 80 fT/√Hz at 600 Hz achieved with SOA.

Abstract

We use a $^{87}\text{Rb}$ atomic vapor, suitable for an optically-pumped magnetometer (OPM) in Earth-field conditions, to study the noise properties of three strategies for generating pulsed optical pumping. We compare a frequency-modulated (FM) laser, amplitude modulation (AM) via an acousto-optic modulator (AOM), and amplitude modulation via a semiconductor optical amplifier (SOA). Pumping the ensemble to operate as a Bell-Bloom OPM, and with an equal degree of spin polarization, the three methods give nearly identical sensitivity, showing that the SOA, despite being an active device, can introduce negligible additional noise. Pumping the ensemble to operate as a free-induction-decay OPM, we observe longer unpumped coherence times with the SOA-AM method than with the FM method. Finally, using the higher power available from the SOA, we demonstrate an environment-limited sensitivity of $80\text{fT}/\sqrt{\text{Hz}}$ at $600\text{Hz}$ and 200fT$200\text{fT}/\sqrt{\text{Hz}}$ at $4\text{kHz}$, one to two orders of magnitude beyond what was achievable with the other pumping methods.